This invention involves a dark, neutral gray colored glass that has low luminous transmittance, particularly low infrared transmittance, and low total solar energy transmittance. Although not limited to a particular use, the glass of this invention exhibits a combination of properties that make it highly desirable for use for privacy glazing such as in the rear portions of vehicles such as vans. These properties include low visible light transmittance to reduce visibility of the contents of the vehicle, low infrared and total solar energy transmittance to reduce heat gain in the interior of the enclosure, a neutral gray color for the sake of coordinating with a wide range of interior and exterior finish colors, and a composition compatible with flat glass manufacturing methods. The glass of the present invention is particularly useful as a substrate for reflective coatings for privacy glazing applications. Therefore, another aspect of the invention is the product comprising the glass of the invention coated with a reflective coating.
The pyrolytic deposition of metal oxide films onto a glass surface is described in U.S. Pat. No. 3,660,061 to Donley et al., the disclosure of which is incorporated herein by reference. Organometallic salts, preferably acetylacetonates, are dissolved in an organic vehicle such as methylene chloride. The organic solution is sprayed onto a hot glass surface where it thermally decomposes to form a metal oxide film which alters the reflectance and transmittance of solar energy by the glass.
It is known from U.S. Pat. No. 2,688,565 to Raymond that light reflecting coatings of cobalt oxide may be deposited by contacting a hot glass surface with an aqueous solution of cobalt acetate. However, such films have a grainy, irregular texture and are highly porous, resulting in poor acid resistance evidenced by debonding of the film.
U.S. Pat. No. 4,308,319 to Michelotti et al. discloses the pyrolytic deposition of a durable, uniform, solar energy reflecting spinel-type film from an aqueous solution of a water soluble cobalt salt and a water soluble tin compound.
U.S. Pat. No. 4,719,126 to Henery, the disclosure of which is incorporated herein by reference, discloses the pyrolytic deposition of light and heat reflective metal oxide films, having similar spectral, physical and chemical properties in comparison with films pyrolytically deposited from organic solutions, from an aqueous suspension wherein organometallic coating reactants typically used in organic solutions are physically suspended in an aqueous medium by means of vigorous and continuous mixing. The organometallic coating reactants physically suspended in an aqueous medium may be pyrolytically deposited to form metal oxide films on a hot glass substrate using conventional spray equipment and under temperature and atmosphere conditions generally encountered in pyrolytic coating operations.
U.S. Pat. No. 4,719,127 to Greenberg, the disclosure of which is incorporated herein by reference, discloses films pyrolytically deposited from an aqueous suspension wherein organometallic coating reactants typically used in organic solutions are chemically suspended in an aqueous medium by use of a chemical wetting agent in combination with extremely fine powder reactants. The organometallic coating reactants chemically suspended in an aqueous medium may be pyrolytically deposited to form metal oxide films on a hot glass substrate using conventional spray equipment, and under temperature and atmosphere conditions generally encountered in pyrolytic coating operations.
Various heat-absorbing glass substrates are known in the art. The primary colorant in the category of glasses relevant to the present invention is iron, which is usually present in both the Fe.sub.2 O.sub.3 and FeO forms. As is conventional, the total amount of iron present in a glass is expressed herein as Fe.sub.2 O.sub.3, regardless of the form actually present. A typical green tinted automotive glass has about 0.5 percent by weight total iron, with the ratio of FeO to total iron being about 0.25.
A typical prior art dark gray glass composition is the following:
______________________________________ SiO.sub.2 72.90% by weight Na.sub.2 O 13.70 K.sub.2 O 0.03 CaO 8.95 MgO 3.90 Al.sub.2 O.sub.3 0.10 SO.sub.3 0.27 Fe.sub.2 O.sub.3 0.060 CoO 0.015 NiO 0.095 ______________________________________
Infrared absorption of this type of glass is not as low as would be desired for the purposes of the present invention. Furthermore, inclusion of nickel is undesirable because the presence of nickel during the melting process sometimes leads to the formation of nickel sulfide stones in the glass. Although the nickel sulfide stones are nearly invisible and cause no harm to the glass under normal conditions, the high coefficient of thermal expansion of nickel sulfide can cause thermally induced stresses sufficient to fracture a tempered glass sheet having a nickel sulfide stone. Additional problems faced when using nickel include haze formation on the glass surface due to reduction of the nickel in the tin bath and change in the glass color when it is heat treated. A more recent, nickel-free version of commercial dark gray glass is disclosed in U.S. Pat. No. 5,023,210 to John F. Krumwiede et al. The colorants in that glass are iron oxide, cobalt oxide, selenium, and chromic oxide. The infrared absorption of that glass is not as low as would be desired, the disclosed examples having infrared transmittances ranging from 34 to 36 percent at a thickness of 5.56 millimeters.
Another nickel-containing gray glass composition is disclosed in U.S. Pat. No. Re. 25,312 (Duncan et al.). The luminous (visible) transmittances for the examples in that patent are higher than desired for privacy glazing.
Other prior art gray glasses containing iron oxide, cobalt oxide, and selenium (without nickel) are disclosed in U.S. Pat. No. 3,723,142 (Kato et al.) and British Patent Specification 1,331,492 (Bamford). In both of these patents the glass is more transparent than is considered suitable for the privacy glazing type of application to which the present invention is directed.
Another attempt at nickel-free gray glass is disclosed in U.S. Pat. No. 4,104,076 (Pons) where, instead of nickel, Cr.sub.2 O.sub.3 or UO.sub.2 are required in combination with iron oxide, cobalt oxide, and selenium. Although broad ranges for the coloring agents are disclosed in that patent, all of the examples have colorant concentrations that would not produce the particular combination of properties desired here. In particular, the teachings of that patent are not directed to production of dark gray glass for privacy glazing.
U.S. Pat. No. 3,300,323 (Plumat et al.) also involves an attempt to produce gray glass without nickel. Instead of nickel, this patent's approach requires the inclusion of TiO.sub.2 and optionally MnO.sub.2, both of which are preferably avoided for commercial production by the float process. Additionally, the objective of the patent is to produce relatively high transmittance glass that would not be suitable for privacy glazing.
Glasses having a color described as "rose-smoke" are produced by the teachings of U.S. Pat. Nos. 2,524,719 (Tillyer) and 2,892,726 (Smith et al.) using iron, cobalt, and selenium as the coloring agents. These glasses are not neutral gray, which is a requirement of the present invention for the sake of color coordination with a variety of vehicle colors and for the sake of avoiding undue color distortion of the view out of the vehicle. Additionally, these patents are directed to producing small quantities of glass for ophthalmic uses, not for mass production of flat glass.
The combination of iron, cobalt, and selenium is disclosed as the coloring agent for making bronze colored glass in U.S. Pat. No. 3,296,004 (Duncan).
U.S. Pat. No. 4,792,536 (Pecoraro et al.) discloses a blue colored glass in which redox conditions are controlled to provide enhanced amounts of iron in the ferrous state for the sake of improving infrared absorption.
It would be desirable to be able to make a dark, neutral gray glass with low transmittance, without troublesome constituents, and that is compatible with commercial flat glass manufacturing techniques. For privacy glazing, it would be particularly desirable for the glass to have very low infrared transmittance, which in turn would yield low total solar energy transmittance.